Fix a crash in cppcoreguidelines-pro-type-member-init related to missing constructor bodies.

Summary: Fixes a crash in cppcoreguidelines-pro-type-member-init when checking some record types with a constructor without a body. We now check to make sure the constructor has a body before looking for missing members and base initializers.

Patch by Michael Miller!

Reviewers: aaron.ballman, alexfh, hokein

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D19270

llvm-svn: 266862